This invention relates to a diphenylsquarylium compound and a filter for display containing the same, more particularly, it relates to a diphenylsquarylium compound which has a sharp absorption waveform having the minimum value within a wavelength range of from 550 to 610 nm in a light transmittance curve and is suitable for using it by containing in a filter for display, particularly in a filter for plasma display panel, and a filter for display containing the diphenylsquarylium compound.
Up to now, various display devices effected by a cathode tube, a fluorescent character display tube, a field emission, a plasma panel, a liquid crystal, an electroluminescence and the like have been developed as color picture image display devices, and they employ a system in which clear color picture images are obtained by combining emissions of the three primary colors of red, blue and green and, at the same time, absorbing emissions of colors other than the three primary colors using so-called band-pass filters. In that case, those in which a pigment is contained are mainly used as the filters, and such a pigment is expected to have no absorption other than the absorption of interest and to show heat resistance, light resistance and the like.
For example, a plasma display panel which is used as a display device of various electronic instruments including a large wall-type television employs a system in which vacuum ultraviolet rays are radiated through excitation of a mixed gas of xenon and neon by their discharge, and the emission of three primary colors is obtained making use of the emission of respective fluorescent substances of red, blue and green by the vacuum ultraviolet rays, but it is known that the neon atom emits so-called neon orange light centering at around 590 nm when it returns to the ground state after excitation, so that there is a disadvantage in that a bright red color cannot easily be obtained due to mixing of the orange color with red color. Particularly regarding blocking of this orange color, since the red color-emitting moiety among the emission of three primary colors is adjacent to around 600 to 650 nm, it is necessary to block the orange light alone while not exerting influence on the red color emission. Contrary to this, with the aim of blocking this neon orange light, various examinations have been made on the use of a filter in which a pigment generally having absorbance at around 590 nm is contained, but the neon orange light cannot be efficiently blocked yet, there are problems such as reduction of brightness of the visual field, and heat resistance, light resistance and the like are also insufficient.
With the aim of solving these problems involved in the filter for plasma display panel, various studies have been conducted by the present inventors taking note of a squarylium compound, particularly a diphenylsquarylium compound, as the pigment to be contained in the filter. On the other hand, an example of the use of a diphenylsquarylium compound having hydroxyl group as a substituent has been disclosed, e.g., in JP-A-10-204304, but according to an examination made by the present inventors, it was revealed that blocking of the neon orange light is still insufficient, because the disclosed compound has the absorption in a range displaced from the wavelength range of the neon orange light. Also, JP-A-2000-43175 discloses an example of the use of a diphenylsquarylium compound having a substituted amino group as a substituent and illustratively describes compounds such as a compound having a dialkylamino group, or a dialkylamino group and acetamide group, or a dialkyl group and hydroxyl group, as the substituent of phenyl group, but according to an examination carried out by the present inventors, it was revealed that these compounds are also still insufficient in blocking the neon orange light.
The invention has been made taking the aforementioned current situation on filters for display into consideration, accordingly, the invention contemplates providing a diphenylsquarylium compound which has a sharp absorption waveform having the minimum value within a wavelength range of from 550 to 610 nm in a light transmittance curve and from which a filter having no reduction of brightness of the visual field can be obtained when it is used by containing in a filter for display, and a filter for display containing the diphenylsquarylium compound.
The gist of the invention resides in a diphenylsquarylium compound represented by the following general formula (I) and a filter for display which contains the diphenylsquarylium compound. 
[In the formula (I), R1 represents an alkyl group which may have substituent(s), an alkoxy group which may have substituent(s), a cycloalkyl group which may have substituent(s), an aryl group which may have substituent(s), an aryloxy group which may have substituent(s), or halogen atom, W in Wxe2x80x94Xxe2x80x94R2 represents imino group, an alkylimino group or oxygen atom, X represents carbonyl group or sulfonyl group, R2 represents monovalent group or hydrogen atom, l and lxe2x80x2 are each independently an integer of from 0 to 4, m and mxe2x80x2 are each independently an integer of from 0 to 4, n and nxe2x80x2 are each independently an integer of from 1 to 5, wherein l+m+nxe2x89xa65 and lxe2x80x2+mxe2x80x2+nxe2x80x2xe2x89xa65, and when two or more of R1 and Wxe2x80x94Xxe2x80x94R2 are respectively present on the benzene rings, the respective R1 and Wxe2x80x94Xxe2x80x94R2 may be different from one another on one benzene ring or both benzene rings.]